had 110 poles of garden allotment and orchard under what he might have vaguely guessed from the aspect I do not consider the ordinary employment of the photographer to involve "a series of very delicate investigations concerning the nature and properties of light," so far as the subject "T. A. has in hand is concerned. All photography can teach on that subject is that the light from such and such parts of the sky has at such and such times a greater or less active power. The conclusions to be drawn from this are by no means necessarily such as "T. A." imagines. ав R. A. PROCTOR. as ornament. FAIRY WHEELS. SIR,-After having read the letter, p. 233, several times, I cannot discover of what kind of stone those discs are made. If they were not so great, I might have taken them for parts of fossil encrinites, but "Subscriber" says none of them were the same size or thickness; they must then have been made by man, cut, &c.; but for what purpose? Two suggestions present themselves. They were intended for throwing with thongs, or lassoes, or for stringing them wearing a necklace, or Very often pierced objects are found in caves, tumuli, &c. Might not these beads, &c., forming part of necklaces, have become, later, objects of exchange -8 primitive money? Might it not be possible to trace by that means the communication ancient tribes had one with another? The note of "Subscriber" affords me the occasion of communicating this idea to my brother correspondents. I hope some other, more acquainted with the question, will bring also his stock of information. Meanwhile I quote a few examples, briefly, Mr. Editor, saying all notes should be drawn up as accurately as possible. Pierced objects have been found in many excavations in France, Belgium, &c., among what are called the remains of prehistoric times. A necklace of human teeth was found in Belgium; in North America, in the tumuli of Columbia River, Walla Walla, many beads, dentalium necklaces, &c., were found. One tumulus in Virginia gave 1700 grains or beads; with the Celtic warrior found in England, near Salisbury, were two fragments of fossil encrinite and a bead of pottery; a Celtic necklace, made of shells, was found near Dijon, in France; many Indians, negroes, &c., have their shell necklaces; remark among them the cowries-in many places at the same time a money and an ornament. The Egyptian beads, necklaces, &c., of so many different substances, are well known to all those who have visited the British Museum. The Chinese have yet pierced metal discs for their money; the English Hong-Kong coinage is another specimen of it. I have said a word, in another number, about the whampum of North America, also a necklace and a money. BERNARDIN. COLOUR BLINDNESS. SIR,-Concerning the remarks of "An Idipot," in your last impression, I have little to say. I have never met with a person to whom red appeared black, and I therefore thought it undesirable to dwell upon that particular form of the malady, though I know such an abnormal vision is repeatedly to be found described in books on the subject, though it is generally allowed that such an anomalous vision is only occasional, notwithstanding Sir David Brewster attempted to show that red colour blindness is most frequently to be met with, and that a normal eye loses its sensibility to red more readily than to any other colour, and that a defect in the vision of any person will be most strongly marked when examined by red light. Though "An Idipot" makes no mention of the fact, I should suppose that the combination of red with other colours does not produce the same sensation of colour that a normal eye perceives. For instance, in a purple the red is not missing, but it appears black, whence it is to be inferred that purple appears as a very dark blue. I would invite "An Idipot "to make some further observations upon his anomalous vision, for it must be admitted that a colour-blind person is better ad apted to form a perfect conception of his defect than a normal-eyed person, and can more readily collect his facts; for let him (the colour-blind) be the inquirer, instead of the witness, and he may collect evidence about colours in every possible shape, from the scientific investigations of the philosopher to the artless remarks of the child. He need not go far for an answer to any question he may choose to put, however abstruse; and as to common facts, almost every one he meets is a competent witness from whom he may gather them. OMICRON. EMIGRATION.-TO "F.R.G.S." SIR,-I am glad to see Cotton Clerk's" letter in the MECHANIC for this week. Let me also appeal to "F.R.G.S." Will he kindly tell me if there is any hope for me abroad, and where, and how? Although a clerk, I think I know a spade, a hoe, axe, prong, &c, when I see one. I am fast learning how many beans make 5, and can already see nearly as far through a stone wall as some people. I am a clerk 37 years of age, married, with 3 children, eldest 10, youngest 6 (both boys). We have saved a few pounds, and could realise a few more, For the last 3 years I have lived 4 miles from my work, I therefore know how to walk. I have RAILWAY CLERK. THE GERM THEORY" AND DEDUCTIONS SIR-The great interest attached to the "Germ These facts I have always thought most interesting, Cold is a well-known arrester of germ development and consequently of their physiological, pathological, and putrefactive effects, but I have never observed it advanced that a rarefied atmosphere may be so alsoalthough of course from quite different reasonssimply from the fact that air of great tenuity will not suspend the germs mechanically and carry them about. If experimental research proves this hypothisis to be correct, I think it may be logically inferred that those diseases which never appear amongst the inhabitants of high altitudes, or are arrested in others upon going to reside there, are really due to, and sustained by, the presence of animalcular life. This is particularly self-evident I think as regards phthisis, and suggests the trial of a simple means for arresting and curing I propose it might be done either by filtering the atmosphere thoroughly before inhalation-much in the way some of Professor Tyndall's experiments suggest-or otherwise, first heating the animalcular air (to a degree sufficient to destroy the vitality of the germs, and consequently multiplying their morbid action) and then cooling previous to using for respiratory purposes. that dreaded disease. Taking for granted that the practical correctness of my theory is demonstrated, let me by way of illustration, suppose that such a building as the Palace of Sydenham, for instance, were applied for utilising it, when hundreds, nay, thousands of invalids could live comfortably and pleasantly together for some months, being all the time quite excluded from the-to them-morbid atmosphere of the outer world, and that thin air supply was treated, previous to introduction into the building, in either of the ways I have suggested. I think the same constitutional effects would be found to be produced-and for similar reasons-as already by a few months' residence at high altitudes. A similar arrangement, and for a like object, might be earried out in hospital practice. Such experiments as would place the correctness of my views beyond a doubt are entirely beyond my BORING INSECTS, &c. In 1832 the Hessian fly, Cecidomyia destructor, destroyed In 1846 another small fly, Cecidomyia tritici, caused in In 1786 the small turnip fly, Hallica nemorum, de- The Bostrychus typographus, or "printer," committed represented, I think, on p. 176, last number, is known in THE EARTH AND ITS FIGURE. are under water? Or lastly, are we to believe that The fact I propose to state is relative to the passage. Then, Sir, when Mr. Beardsley has made acquainted before. EXTRACTS FROM CORRESPONDENCE. RUSHES. - "Bernardin " says: "In reply to TIONS.-"Vibrator" writes:-"I was rather sur- INDUCTION COIL.-ANSWER TO "SIGMA,”— TESTED RECIPES.-" A. Boughey" writes:-" A Preston" says:-"I can recommend the "Phantom" Spider in the ENGLISH MECHANIC is quite inap- conical points, even in the best work. Cylindrical pivots are READINGS FROM THE GLOBES.-"Ab Initio" writes:-J. Dyer, p. 235, in attempting to correct T. S. H.' appears to me to confound the words sun and time with each other. Philadelphia, for instance, has its time 5 hours earlier than London, it being only 7 a.m. there when it is noon here." REPLIES TO QUERIES. [2528]-MUSICAL BOX.-I must apologise to Harry Bertram for too severely criticising his description, which, however, I said was well repeated as far as the lesson was learnt. He means that the end of the roller has a flange which moves in the notch of right lever. This may be the case in very common boxes that only play two tunes, and I do not think would act for three; and it is bad, as it enables you to shift the barrel while playing, which has a bad effect, or even to shift the barrel when not playing, which is destruction to the box. In good boxes it is done by a wheel of the same number of teeth or rather spokes (and no rim) as the number of tunes to be played, which is fixed between the barrel and the first toothed wheel, only fixed eccentrically near the outside of that wheel, and every time it is carried round by the barrel turning, one of the spokes is caught by a fixed stud, and is held by it till the next spoke comes to the right place to be itself caught by the stud at the next revolution of the barrel. On the boss of this spoked wheel is a short piece of a screw or a camb which keeps pushing the barrel further and farther until the end of the camb is reached, when a spiral spring pushes the barrel back ready for the first tune again. The music is not stopped by the L-shaped lever dropping into the hole in the end of barrel, but when it does drop in, the curved arm shown in the drawing, p. 164, on the opposite side to the hook, catches hold of one fan of the fly and stops the works. It is a fan-fly not a fly-wheel, as it is not a wheel at all.-J. K. P. easier to catch the centre of that small ring than if he made [3707.]-TWISTING POWER OF SHAFTS.-The relative 1 = 1.75 = 20; 1 and a shaft to be equal in strength to a cast-iron one, must 1 cast steel --. 8 25 9 Q. Q, R. follows: Area of flat valve = 42 x 7854 = 12.5664 sq. in. The area of the concave valve may be found by adding the [2639.-OPINIONS WANTED. Thanks to Mr. Har-square of the radius of the valve (2in.) to the square of the rison for his advice about the links and the eccentric. When the lever is in the centre notch the valve spindle end is in precisely the centre of the link, and the eccentrics are properly set, but I think he is wrong when he says the link ought to vibrate on the centre without imparting any motion to either spindle or valve, for I have noticed several since, and they all work the valve a little, but not enough to open the ports, which is caused by the action of the two eccentrics one against the other. If our paper is an International Mutual Improvement Society I am surprised that the subject has not been taken up by more of its members.-JOHN W. BEDFORD. [2640.]-GIRDER PATTERNS.-In "N. L.'s" answer to my query he says that making the pattern bent would not do much good, as the moulder would ram it out of shape. Now suppose the girder to be 40ft. long, section as per sketch (Fig. 1), bottom flange 24in. thick, rib 1fin. thick, how will he ram down the ends, and if he can bend it to suit his requirements is it not just as possible to make the pattern bent, and so save time, and with more surety, for what is to prevent the ends from springing out again, as it would be moulded on its side? Again, a gutter of this section 28ft. long (Fig. 2), thickness at A 4in., and at bottom fin., which would be moulded on a block to At the inside, how would he bend that, and what weight would he require on the middle to keep it down, as it would be moulded with the bottom downhill. And again a foundation plate 33ft. section (Fig. 3) thickness of side A B C D fin., and the top 14in., moulded with the top or round side down hill; and lastly one of a smaller pattern, a tile plate bearer for malt kiln floors of the same size (Fig. 4) section, thickness at point of web fin., A at top B Sin., and thickness of top flange in. and 4ft 6in, long, which he might bend in the pattern with a bit of trouble and some weights to keep it there; but which would be safest, his plan or to make the pattern bent? And then he finishes by saying that it is a question whether one [2675.-POLISHING PIVOTS.-The ridges mentioned by "C. R." are caused by the polisher having the side that polishes the shoulder too much inclined to the side that polishes the pivot. It ought to be nearly at right angles. Pressing too hard against the shoulders has also a great deal to do with it. The polisher ought to have a side as well as a length motion given to it now and then, to cross the marks as it were. The bow takes long strokes, while the polisher moves very little; and always contrary to the direction the pivot turns. "Cylinder" will do well to attend to the above; and I may add, in answer to his query, the conical pivot he marks B is used only for good and best work, in holes furnished with endstones. Cylindrical pivots with the shoulder bevelled off are for more common work, though I have never seer but once or twice a Geneva cylinder with 0-4417, the difference of the areas of the two that the quantity of water discharged by a syphon will be any: D= diameter of pipe in feet. [3744.]-SILVER COIN.-I think there are errors in the part is 1in. in diameter, at the shoulder of the handle part it is 2in., a groove wide is turned in the plain part, which allows the bolt D to pass through, and act as a sort of garter pin, to cause the two checks to recede from or approach each other; the bolt Dis of iron square, and bevelled out to square at the bottom, so as to grip the knife F, which has a square hole, bevelled, to match the bolt. E is a nut, which screws down on a lozenge-shaped piece of iron, so as to grip the knife very tight. CC are two guide rods 13in. long, square, firmly fastened into the cheek A, the handle of the screw is 5in. long, as the knife cuts the handle should be gradually turned, so as to keep the knife to the work.-AB INITIO. [3765.]-NAVAL ARCHITECTURE.-" G. E. J." should write to C. W. Merrifield, Esq., (Principal of the School of Naval Architecture,) South Kensington Museum, who will give him any information he may ask for as to the evening classes. R. M. [3768.J-POISONING BY CANTHARIDES.-I am very sorry to see "M. D." states in page 237, Vol. XI. that the effects of cantharides are only transient, &c. They are not so; in small doses it is an irritant of thebladder; in larger or improper doses it produces serious bleedings often resultidea that it is provocative of physical love, for which purpose ing in death. It is administered surreptitiously under the it is absolutely useless. No man conscious of his moral responsibility would ever administer it, excepting under and in strict accordance with the orders of a well qualified medical practitioner. I believe any person administering it for improper purposes is liable to a criminal prosecution.-E. DEACON. [3772.]-OLD COINAGE.-Old copper coins may be sent to the Master of the Mint, Tower-hill, London, who will, no doubt, take them at, I believe, their full value.-R. M. CAMERA.-If [3773.]--PLATE PHOTO "Snatch Block" will tell me whether he wants to make a portable camera, or one for the studio, I will tell him how I made mine. Of course, if the Editor, be agreeable, I could describe both. 4-plate is not too small to begin with.-MUS. [3774.]-LOOSE PULLEYS, &c.-The best plan will be to bore the pulleys about fin. larger than the shaft, and sweat a brass bush in it, or one composed of the following alloy:have proved the latter to be a very good wearing metal.(Babbitt's metal) tin 10 parts, copper 1, and antimony 1. STAEM. [3774]-LOOSE PULLEYS, &c.-Wm. Corlett should turn the shaft end true, then bore out the loose pulley, and let the pulley work on a loose bush, bored and turned to fit the two, with a small collar and set pin at the outer end for fastening on the shaft; this would be a much better job than any composition, and is a very general thing nowadays; cast iron and cast iron would then work together, which is to be desired.-MUTUAL IMPROVEMENT. [3774.]-LOOSE PULLEYS, &c.-When worn in, the hole should be bored out sufficiently large enough to allow substance for the bush, which may be good gun metal, and will wear very well; the bush should be pressed in tight, that it may not move in the hole, and when it wears out, which will not be for a long time, if properly oiled it can be knocked out, the pulley.-JONATH. and a new bush put in without doing anything to the hole in [3776.]-BOILER SAFETY-VALVE.-"One in Need," has not given quite enough information to enable me to answer his question exactly. Does the weight of valve and lever, as stated by him to be 74lb., give the true pressure exerted by them on the valve when in place? I expect not, and should [3745.]-STEAM PIPE JOINTS.-I always use loz. of sal imagine their effective pressure on the valve to be at least ammoniac to every llb. of borings, with just a dash of sul-211b. Since the area of a 3-inch valve is 7 square inches, phur to quicken it in hardening.-ANTI-EGYPTIAN. this will give 3lb. per square inch. So the weight will have to balance only 571b. per square inch, and will be found thus:7 sq. in. × 57lb × 3 in 20in. + Stin. [3776.]-CASE FOR FERNS AND MOSS.-The best form is to make the legs and upright rods which hold the glass in one length, with a light rod running round the top, in the underside of which is a groove, There should also be a groove on the top edge of the box which holds the soil, and the glass made to slide on one side to allow the plants to be at [3746.]-TESTING BOILER.-It will be of no use of Thos. Edwards testing his boiler without he can see the surface and seams of all his plates. If his boilers are only single rivetted, he cannot work them at more than 15lb. pressure. I had two boilers which I worked at 15lb. pressure. I had my boilers tested to 120lb., indicated by Bourdon's pressure gauge; they stood it better than they could be expected, although they (the engineers) will not allow them to be worked with more than 15lb. pressure, being single rivetted boilers.-ANTI-EGYPTIAN. [3750. SILVER COIN-"A Beginner" will see his -F. H. [3755.]-TURBINE WHEEL.-" Senex seems to have asked me almost the same question as I have asked him, which was, what quantity of water and height of fall was necessary to drive an one-horse wheel. However, as near as I can get at it, the fall would be 20ft. through a pipe of in. internai diameter. I would also ask what height of fall or pressure of water is termed high pressure, as in some street mains ?-A. B. [3757.]-A BOOKBINDER'S PLOUGH.-Enclosed is a sketch on the scale of of an inch to an inch, A A is the right hand cheek of the plough, 10in long by 4 high, 1 thick; the left hand cheek is of the same di It coal at 288. per ton, for less than 2s. per week. At present we process the carburisation of gas by causing it to pass through a vessel filled with some hydrocarbon, this plan has been tried under two or three patents for the last 30 years, but nearly in all cases where it has been adopted, after a long trial it has been abaudoned on account of the difficulties, and the absence of the economy anticipated. A word respecting gas regulators, and regulating burners:-The best regulators for fixing near the meter that I know of (and I have tested several) are those regulating burner. Nearly all the regulating burners offered made by W. Tices, 65, Bartholomew-close, E.C., and by W. Sugg, Vincent-street. Westminster; Sugg has also a good to the public are worthless after they have been in use for a short time,-L. M. glasses can be easily removed for cleaning, &c. A hot water tank in the bottom heated with a small gas jet underneath will make a tropical stove on a small scale, or a hot water, pipe round the inside, and a small copper boiler underneath will do even better. I have one, and for two years have grown with success the rarest tropical plants, orchids, &c. One year I had orchids only, the next I had caladiums, Egyptian papyrus plant, dwarf palms, tree ferns, &c. Now I have aquatic plants from the Amazons and Borneo, pitcher plants, &c. costs me little or nothing, as the plants always increase in value, and I have no difficulty in exchanging them. So far as treatment goes, he will learn more from the persons he buys his plants from than any one else, as each plant has peculiar habits. The case should have a reasonable amount of ven[3794.]-POLISHING STEEL.-"Cylinder" must be sure tilation, so there is no need for care in fitting the glasses and this clock is good metal, that his stuff is good, and that his woodwork closely; mine is open in. at every corner all the steel was properly hardened before it was tempered, and not way up, and we burn a large quantity of gas in the room empered too much. He must have everything clean, and not without the slightest effect on the most delicate plants; if attempt, the least quantity of red stuff used, and the polishing reaching to the top of the water like so many juvenile palm dust flying about. The block must be refiled before each they are quite close they get mouldy.-A DENTIST. [3779.1-BOILER." One in Need," should give the effec-cult to describe, as it is by the feel he will know when he has moved very little during the process. Anything more is diffirubbed enough. It all depends on leaving off at the right tive weight of his lever, and the weight of the valve; if he is unacquainted with any method of finding the same, he may get it as follows:-Place the lever at the fulcrum on a three 204 sided file, and fix the short end, at the centre of motion, hang weight sufficient to balance the long end, thus the effective weight is the weight required to balance, and the weight of lever, to which he must add weight of valve.-JONATH. MENT. [3779.]-BOILER SAFETY VALVES.-According to "One in Need's" figures, the weight required on end of lever would be 671b. 10oz., but I am afraid the 71b. 14oz. weight of lever and valve does not include the effective weight of lever, in which case he is altogether wrong.-MUTUAL IMPROVE [8779.]-BOILER.-A weight of 58-184lb. placed on the end of the lever will give the required pressure. This weight is not exactly correct, but it is as correct as can be calculated from his description of the valve. If he requires the exact weight, he must give the weight of the valve and lever separately; if the lever be of the same breadth and thickness through out, its effective pressure can easily be calculated, but if tapered he must disconnect it, and try what weight will balance it, making the point in a line with the centre of the valve, the fulcrum.-THOMAS J. O'CONNOR. The [3793.]-COOKING BY GAS.-If the gas is not under the meat inside the oven, the meat is quite as nice as that done before the fire. We find the best way is to put a Bunsen burner under an iron plate and cover this with a large tin cover, which is cased in flannel to prevent loss of heat. meat must be supported on a stand in the centre of this, with the gravy tin under it. By this arrangement the meat is cooked as before the fire by hot air, and the most critical person cannot tell how it has been cooked. The same burners may be used for boiling vegetables, &c., and plates may be warmed by setting them on edge round the oven, or putting them on the top. We have used this plan for 6 years exclusively, and as near as we can tell, it costs about 5d. or 6d. per week to cook for 3 people. During 6 months of the year we have no fires at all,a ndo f eking cannot be kept with moment.-NOBODY. [3797.]-TELESCOPE STAND.-If Mr. Turton will call [3801.]-LEVER ESCAPEMENT.-"Gracchus " asks for [3803.]-CHANGING COLOUR OF PRIMROSES.-I have about half a dozen differing in colour from vellow to a very dark purple. This change was caused by being yearly transplanted into richer soil. They first come an orange colour, then a light red, and eventually purple. The follow ing recipe will show "J, D. M." how to change other flowers:-The colours of flowers may be changed by certain additions to the soil in which they grow. Powdered charcoal deepens and intensifies. The flowers of the dahlia, rose, petunia, &c. Carbonate of soda reddens hyacinths; and superphosphate of soda alters in various ways the hue and bloom of other plants.-W. F. HAIGH. [3810.]-CYLINDER PATTERN.-Let amateur make his cylinder model similar to sketch, the main feature of which is the valve box and thoroughfare cores. In the first place, put -JOHN W. BEDFORD. [3813.-POROUS CASTINGS.-This short query would admit of a very long answer; but I will try and make it as plain as I can. 1st. The sand is a very important thing; if it contains too much clay it is a great difficulty to make castings free from airholes. Clayey sand is only fit for light castings, where good impressions are of value, likewise avoid everything that will generate gas, such as coaldust, charcoal, and like substances. Ram your mould regular, and vent or pierce it with innumerable airholes; cast or pour it with as hot metal as you can get, not forgetting to run it in the mould as quick as it will go in. The sullage must be kept back with a skimmer during the pouring of the metal in the mould, and the head or git must be made so as it will be kept up or kept full during the casting operation.-N. L. [3819.]-CHEAP GAS.-A great saving in the consumption of gas can be effected by regulating the pressure of gas on the burners. When more gas flows to the burners then they can properly combust, the illuminating power of the gas is deteriorated, and, of course, the gas bill is increased. One of the best ways to prevent this waste of gas, is to have a good regulator fixed near to the meter, which would regulate the flow of gas to all the burners. Another plan I have also adopted, that of placing a disc, with a small hole in the centre for the gas to pass through, in the elbow or brass socket in which the burner is screwed. The whole in the disc must be made according to the size of flame required at the burner. I have been able to save 25 to 30 per cent. in the consumption of gas by adopting the above. With regard to Soldier plant. There is no plant so beautiful and interesting [3820.]-AQUATIC BOTANY.-Stratiodes Alviedes, or as this for the above purpose. Tie it to a stone and sink to the bottom; it will soon send up young plants on long stems floats free, of a lovely transparent green. They will soon trees. After a time the stems decay and the young plant require thinning out; for this purpose a tank should be kept out of doors, in full sunshine, where those not wanted should brown. Returned to the aquarium they will gradually go be placed, when they will get strong and change to a mahogany through all the intermediate shades till they regain their green hue, A constant interchange of tint may thus be kept up. The plant may be grown of any size, according to that of the vessel, and increase abundantly.-AMATEUR. [3824.] GOVERNORS.-I can recommend Porter's patent governors as being very sensitive and powerful. They revolve very quickly-usually from 300 to 400 revolutions per minute-and when properly proportioned will not allow a variation of more than perhaps 3 per cent; so that a shaft running at 60 revolutions per minute would not vary more than 2 revolutions per minute. These governors are made by the Whitworth Company, in Manchester.-Q. Q. R. the nitrate of silver stains, pour on solution of potassic iodide, [3834.]-DUMB BELLS.-See "Physical Education." by A. Maclaren of the Gymnasium, Oxford. Clarendon Press Series, 5s.-OMIO. [3836.]-PITCH OF PROPELLER. The first thing "T. J. O'C." must do is to bore out the eye of the propeller in the lathe, and fence np the outside end of the eye for the nut to bear properly that secures the propeller on the shaft; then take it out and lay it down on the ground with that side up that is faced for the nut, and level it up all the four ways of that part that is faced; then put a centre into the eye of the propeller, and from the centre of the eye draw a circle with any radius ou that part of the eye that is faced for the nut, and divide that circle into 12 equal parts, and also divide the blade from the centre of the eye to the point into feet, and draw the lines across the blade with a radius from the centre; then take a straight-edge that will reach from the point of the blade to over the centre, and lay the edge of the straight-edge on the point where one of the divisions cuts the and keeps it in that position by laying a block of iron on it; circumference of the circle and makes it run into the centre, then plume down from the edge of the straight-edge with a centre plummet to the divisions on the blade, and mark them with a centre punch; then measure the distance from the edge of the straight-edge to the plume point on the bladepresume that it is 6in.; then turn the straight-edge to the next divisions, still keep it running into the centre, and iikewise level, and plume down with the plummet again to the blade, and mark it, and then measure the distance down again from the edge of the straight-edge to the plume point-presume it is 20in. Now the difference between 20in. and 6in. is 14in.; then as every inch of the perpendicular distance gives 1-12th of the pitch in feet, therefore 14in. would be a 14ft. pitch to the blade of the propeller; and if the blade is not broad enough to take in a twelfth part, divide the circle into 24 parts and the blade into 6in., and every in. in the perpendicular distance, in the same way, will give a twentyfourth part of the pitch, and so on. The most convenient way to divide the blade is to divide the straight-edge into feet or half-feet, as it is required, and square lines across the edge; then make one of the lines coincide with the centre of the propeller, and the edge with one of the points on the circle, and then plume down from these points to the blade and mark them; then measure the distance down.-G. B. D. Flautist's" inquiries respecting the Boehm flute, I may [3845.]-BOEHM FLUTE. In answer to "Another state that the use of the rings is to stop holes which are beyond the reach of the fingers. On the old flute the holes fingers to reach them; hence its notes are unequal in power, are altered from their true position from the inability of the and are "out of tune." The latter defect is partially lessened by altering the size of the holes, but at the expense of adding to the former. Boehm overcame these difficulties by placing the holes in their natural places, and by making them of equal proportions throughout (the holes being made gradually smaller and smaller through a regular progression upwards), by which means he obtained uniformity of force and tune, and great increase of power in the whole scale of the instrument. But these advantages were met by a great drawback, for he found it necessary to alter the fingering of many notes; and this involved to those who already knew the old flute the unlearning of one system of fingering and the learning of a new. From this cause many, seeing the superiority of the Boehm flute, became dissatisfied with their old flutes; but finding the difficulties of the new fingering too much for their patience, gave up flute-playing entirely. Some few years ago Mr. Clinton, the celebrated flautist, invented a flute called the "equisonant flute," which not only had all the advantages of the Boehm flute, but retained the old fingering, and with increased beauty and brillancy of tone to the instrument itself. The writer of this has had practical experience of all these flutes, and much prefers his "equisonant" to any other. What I have said about Autes will equally apply to B clarionets. It would take too much space to describe flute machinery thoroughly.-H. T. LEFTWICH. [If Mr. Leftwich desires to treat the subject more fully, space is at his disposal.-ED. E. M.] [3846.]-NICKEL.-The following extract may perhaps be of interest to "Another Flautist " :-"Nickel (Ni 29-57), a metal of a greyish-white colour, with remarkable magnetic [3850.]-THERMOMETER.-"Thermo" had better place his thermometer against a piece of ice, which will have the effect of causing the mercury to recede towards the bulb; but if the bulb is not broken much, it will soon settle of itself. -SEMPER PARATUS. 8851.-HARNESS.-"Equestrian" will find the best way to elean his harness is to well wash it in warm soap and water, (soapsuds would be better), dry it thoroughly, and then rub neat'sfoot oil on it; let it stand till next day, and if it absorbs the oil readily, give it another coat. This treatment is suitable for any kind of harness or leather; but if the bridle is a black one, he will find a great preservative in Harris's harness composition.-SEMPER PARATUS. [3852.] BRASS INSTRUMENTS.-They fill the tubes with melted resin, and twist them about when cold with apparently as much ease as they would use in bending a piece of cord. No doubt a sharp look out is kept for puckers, which they hammer in directly they appear on the inside of a bend of course with a small round-faced hammer. Copper tubes may be filled with lead, but it is dangerous with brass ones, as, to get the lead out, a good heat must be used, which makes brass brittle, and very likely to give way with the weight of the lead. I saw Distin's factory once, and was quite struck with the tube bending, which I had supposed such a delicate operation. I believe it is very difficult to get bruises out of tubes, and that they have a sort of jointed metal mould to put inside a bell which has a bent tube to it, and which has received any injury.-J. K. P. [3852-BRASS INSTRUMENTS.-The bends of brass instruments are made by first filling them with lead, and then bending them; after that the lead is melted out. The reason they require filling with lead is to keep them from bulging out at the sides. The lead would, however, be inadmissible in the case of zinc tubes, as they would melt when the lead was run out. I am told resin would do instead, but this I have not tried. I should advise "Clutha" to try it, and report progress.-SEMPER PABATUS. [3860.]-COPPER COIN.-Is of Catherine II., Empress of Russia; no value.-BERNARDIN. [3863.-PASTILLES.-Take 8drm. of cascarilla bark, 4drm. of gum benzoin, 2drm. of styrax, 2drm. of olibanum, 6oz. of charcoal, 14drm. of nitric, and a sufficient quantity of mucilage of tragacanth. Powder the substances and form into a thick paste with the mucilage, and divide into small cones; dry them until quite hard in a slow oven.-MINNEHAHA. side to be bored out to make stuffing box, and a small boss [3866 J-LATHE AND ITS USES.-For the information Mount-street, Grosvenor-square, W. [3867-]-LATHE DIVIDING PLATE-If you look at P. 12 of present volume, you will see a counting index figured and described in connection with the wheel cutting engine. It is not very troublesome to fit up, and need not be self acting.-J. K. P. [3868.3-WATERPROOFING CLOTH.-Make a solution of india rubber in naphtha, and apply it to the cloth; this is the article used for waterproof coats; add a little linseed oil to it. If this is not suitable to "A. S. A." I can send a few other recipes.-SEMPER PARATUS. closer look at the group on page 63 of "F.R.A.S.'s" maps. He wants a sketch of the Pleiades; I refer him to his own on page 238 of present vol.-H. W. BISHOP. [3876.]-TOOL FOR TURNING PIVOTS.-The latest tool for turning pivots is the French turnbench, with 8 centres and a small slide rest. They are from 10s. 6d. each and upwards.-S. TANENBERG, Leeds. [3878.)-DAILY TEN O'CLOCK TIME SIGNAL.-Yes; all wires from 1min. to 10 o'clock to 1 min. after 10 are in conection with Greenwich clock, when all working is suspended for that time.-A TELEGRAPH CLERK. [8879.]-GINGER BEER.-White sugar 10lb., lemon juice 9oz., honey lb., bruised ginger 11oz., water 9gal. Boil the ginger in legal. of water for half an hour, then add the sugar, juice, and honey, with the remainder of the water, and strain through a cloth. When cold add the white of one egg and oz. of essence of lemon; after standing 4 days bottle. Extracted.)-MINNEHAHA [3897.1-NAPOLEON,-I beg to inform "H. B.", p. 231, that his coin of the French Republic, 1848, is not worth much more than its weight in gold. If it is, as I suppose, a 20 franc piece, its intrinsic value is 15s. 104d. in our money.HENRY W. HENFREY, M.N.S., &c., &c. Now [3900.] ASPHALTE FOR ROOFING, &c. - I would advise" Dublin Printer" to try the following; he will find it useful in stopping many a crack besides those in his roof:Take 2 parts by weight of common pitch with 1 part of gutta percha, melt together in an iron pot; it forms a homeg eneous fluid much more manageable than gutta percha alone. to repair his gutters, carefully clean out of the cracks all earthy matters, slightly warm the edges with a plumber's soldering iron, then pour the cement in a fluid state upon the cracks while hot, finishing up by going over the cement with moderately hot iron, so as to make a good connection and a smooth joint. The above will repair zinc, lead, or iron gutters, and is a good cement for aquariums.-PATIENCE a AND PERSEVERANCE. [3907.]-UNIVERSITY EXAMINATIONS.-London, 1871. [3869.]-WEIGHT OF WATER. -The reply to "Country-Special subjects:-1st B.A., Latin, Tacitus, "Annals," man's" query is very simple. By a rule in hydrostatics, any Book I.; Virgil, Eneid," Books VII. and VIII. English, body immersed in water is pressed by the weight of a column History of English Literature during 17th Century; Bacon, of water the height of a perpendicular drawn from the centre of gravity of the body to the surface of the liquid, and in Mirabilis," and "Absalon and Achitophel; " French, English, "Essays;" Shakespeare, "Julius Cæsar; " Dryden, " Annus breadth equal to the cross section of the body. A rnle to calculate the pressure on the bucket may be stated thus: for pest and present. If "Xanthos" will write to me, I will every 7ft. of depth allow 3lb. pressure per square inch.give him any information he may require upon this subject. (3863)-PASTILLES.-"W. R. C." asks for some recipes for fumigating pastilles; I send the following, copied from a book which I believe can be relied on, but not proven on account of the difficuity of obtaining one or more of the components:-Pastiles á la rose. Essence of roses 1 part, nitre 9 parts, gum 12, tears of obanum 12, tears of storax 12, powder of roses 16, charc al 60; powder the solids very fine, and make a paste with gum tragacanth, 2 parts dissolved in rosewater 35.-Pastilles à la-Vanille: Gum galbanum 25 parts, tears of olibanum 25, tears of storax 25, nitre 25, cloves 25, vanilla 35, charcoal 115-make paste as above.-Orange Flower Pastilles: Neroli 1 part, nitre 9, galibanum 13, tears of olibanum 12, tears of storax 11, pare orange powder 12, charcoal 70, reduce to fine powder, and make paste with gum tragacanth 2, dissolved in orange-flower water 15, and rose water 17 parts.- Lastly, but hardly fit for a sick room, Explosive Pastilles: Make a hole at base of pastille and fill with gunpowder. I am afraid the queer names of these fragrant resins will almost frighten the querist; but I believe all except tears of storax and neroli can be bought in penny worths at the druggist's; if one shop does not keep them, try another. They say that tears of storax have not been in the English market for vears, but I believe the liquid storax will answer the purpose. By the word "tears" is meant the drops of resin in that shape, but of course the lumps will do as well. Orange and rose powder I take to mean pow-A BOUGHEY. dered orange and rose flowers. Neroli is the essential oil of orange flowers. I will now give a simpler way for fumigating, but which has this objection, that everybody does not like the perfume. Dip brown paper till quite soaked in a strong solution of nitre; then, when perfectly dry, rub over it a varnish made by dissolving either or both gum olibanum (frankincense), and gum benzoin this soon dries and is ready for use; this last I have done myself, and succeeded in getting a strong fumigant, -H W. BISHOP. [3871.]-THROTTLE VALVE.-I send for "Grocer's" benefit a full size drawing above of one I put to an engine of 4 cylinder. The same thing reduced to gas barrel which measures say inside and the casting bored to 1" would do for a 1 h.p. engine. The lower section of pipe is screwed and brazed into wrought iron flange and faced off in the lathe being a short length altogether, the upper flange cast iron apped for barrel, which is screwed, in with white lead. The intermediate piece is like a pulley with large hole through, and very deep gro with a piece stuck in the pattern at one [3869.]-WEIGHT OF WATER.-It is said that any heavy body 201b. in weight, taken to the top of a mountain 3 miles high, loses but oz. in weight; therefore the difference in weight of a bucket of water at the top and bottom of a well 90ft. deep, must be indeed slight. The apparent difference is, I think, due to the weight of the rope when the bucket is at the bottom.-HARRY G. NEWTON. [3873.]-BOOKBINDERS' GLUE.-Bookbinders use the same glue as carpenters and joiners, but break up the cakes into small pieces, and soak them in water for 8 or 10 hours, then thoroughly melt them in an iron or earthenware pot before using in the glue pot; some add treacle when using it for cloth work; some add paste. There is a work called "Bibliopegia," I think it is by Arnott. I do not know the publisher, but if " Aristotle" will insert his queries in "our" MECHANIC, they will receive prompt attention from-AB INITIO. [3874.1-CONSTELLATION.-The group "Aristotle" sketched is the Pleiades, as he will at once perceive on a C. H. W. B. [3908.]-OLD COPPER COIN.-In answer to Mr. Nash, p. 239, the inscription on his coin is FAVSTINA AVGVSTA Faustina Empress). I cannot say without seeing the coin whether it was struck by the elder Faustina, wife of Antoninus Pius, born A.D. 105, died A.D. 141, or by the younger Faustina, wife of Marcus Aurelius, died A.D. 175. The bronze coins of both are common, and worth very little.-HENRY W. HENFREY, M. N.S., &c. CHINESE VACCINATION.-It may be news to some that the Chinese commenced to practise vaccination for the small-pox at Canton forty years ago. There are now public vaccinators at Pekin with regular days and hours for scarifying infants brought to them, just as in London. When their supply of vaccine lymph falls short, it is renewed from the English missionary hospital. NOTES AND QUERIES. [3910.]-CONICAL WINDING DRUMS. Will some brother reader kindly give some particulars respecting the construction and working of conical or spiral drums, as applied at collieries for drawing coals, and state what conditions are to be observed in order to ensure their safe working ?-W. M., Junr. [3911.]-GALVANIC CELL.-I have a galvanic cell, composed of a stick of what I suppose to be carbon (it is black, about 5in. long, and lin. square) in a porous evlinder surrounded by a zinc cylinder about 3in. in diameter, all in a glass vessel. Will any of your readers kindly inform me what fiquid or solution I should use to excite it; also the name of the combination, and whether it is best adapted for strength or constancy ?-HERMIT. Can [3912]-REVOLVING FRAME FOR SHOP WINDOWS. -I wish to construct a revolving frame to show pictures in a shop window, and find the ordinary meat-jack clumsy; it revolves too rapidly at times, and requires winding up during the day; I should like also to avoid the return motion. any of your correspondents help me?-PITMAN. [3913.]-TO A. STRINGER-In No. 269 A. Stringer writes on velocipede construction; will he kindly, for my own and the information of others, insert a plan with the details of the three-wheeler he speaks of steered like a boat; will he also say where I can purchase an "English" velocipede?-CON STANT SUBSCRIBER. [39141-WOOD ENGRAVING. I should feel greatly obliged if any brother subscriber can tell me where to obtain the best book of instruction in the above art, and the price? -K. T. Z. [3915.]-NAIL BAGS.-I have a large quantity of nail bags which are worn out, for what purpose will they serve; will they do for making paper, or must I consign them to the rubbish heap?-W. CATTELL. [3916.]-PAINTING BOILER.-How can I mix a good green paint to paint the boiler of an engine so as the heat may not effect it ?-A. W. [3917]-ICE CHEST.. ICES.-Perhaps some of my fellow subscribers will tell me the best plan for making an ice chest (a few sketches would be a great assistance); also a few instructions for making ices?-BRIGHTON SUB. [3918.-ENAMEL.-Can any of my numerous brother readers inform me how to make white English glass, or the tin enamel, as made in France, that given a few weeks back was not white or good; also where I could obtain a brush for painting figures and letters on clock and timpiece dials?ANXIOUS INQUIRER. [3919]-GALVANIC BAND-TO "SUFFOLK AMATEUR."I have very carefully made a galvanic band after the plan of "Suffolk Amateur," p. 11, last vol., I have tested it with a small galvanometer, but cannot get the slightest current from it. I have made it as follows:-A strip of copper and one of zinc, 18in. long, lin. broad, and 1-32th in. thick, are united at the ends by small copper rivets, I have lapped over these rivets with thread, and varnished over the thread with shellae in alchohol, the ends are left bare 14in., the copper and zinc are lapped spirally round with a piece of cotton list lin. broad, and covered in a bag of oil skin; I tried all strengths of vinegar, but to no purpose. Would "Suffolk Amateur" kindly say where I have failed?-W. A. [3920-MEASURING LIVE STOCK-Will some of your learned correspondents inform me if their is a book published on measuring live stoek, say an ox; or give a rule, through the medium of our MECHANIC, to measure a living fourfooted animal so as to find its weight?-A COUNTRYMAN. [3921. BRASS COIN.-I have a brass coin the size of a penny, on the obverse the bust of a man, on the reverse a female in chariot drawn by four elephants with LIE over them, there is an inscription round the bust, but the only letters I can make out are ALT-PAIANC. I should like to know of what coin it is, and of what value ?-TOM C. HOLLOWAY. [3922.] REMOVING PAINT.-Although some answers have appeared in reply to inquiries for a good alkali or such method for removing paint, still not one effectual mode has been suggested. If any brother reader could advice a ready and effectual method of softening the old paint on dorrs, &c., when it becomes thick and hard, so as to remove it speedily (without the use of charcoal fire), and enable the operator to clean off mouldings with credit, it would be a very useful enlightenment?-HOUSE PAINTER. [3923.] GEOMETRICAL DRAWING. A method of drawing the ellipses that represent circles-N.B.-When the dimensions are not reduced to geometrical proportion; if one can also recommend a good cheap work on the above P-CARL J. H. COTTHESSON. [3924] SILENT FANS,-Can any of our readers tell me the diameter of the blade of one of Messrs. C. Schiele and Co.'s 50in. Excelsior silent fans, patented 1863 ?-ONE WHO WANTS TO KNOW. [3925.] POSITION OF MAGNETIC POLE Can any of our readers inform me whether, as the declination of a needle is the angle made by the magnetic and geographical meridians of any place, and the magnetic meridian passes through the magnetic poles, when the declination nia, as places suitable to make a home in, particularly as to [3981.]-INDIA RUBBER SOLUTION. — Will any of [3932-BICYCLE RUBBER TIERS.-I intend fitting an india rubber tier to the driving wheel of my bicycle, could any brother subscriber kindly assist me in the fixing? I do not want to remove the iron tier; should also like a practical opinion of the merits of the rubber tiers, best shape, depth, &c.?-C. MORTIMER. [3946.]-SYRUP OF HYPOPHOSPHITE.-If any medical correspondent will inform me of the medical uses and cost of syrup of hypophosphite of iron and quinine, together with the dose for ailments in which it is beneficial, I shall feel greatly obliged ?-G. THICK. [3947.)-REMELTING HARD WHITE PAINT.How shall I remelt hard white paint, shelled off, composed probably of white lead boiled oil, and litharge.— T. S. U. [3948.]-INDIA-RUBBER TYRES.-If some correspondent, who has had experience with india-rubber tires, on velocipede wheels, would answer a few questions respecting them, they would oblige a aumber of readers who are interested in velocipedes Where they can be obtained, and price? The best way of fastening them on, and should they be used with iron tires? How long they last? How are they astened on the "Phantom" wheels?-G. K. Guyana? A few particulars will oblige.—JOHN D. [3949.]-GUYANA.-Where is situated the Republic of [3950.]-GOMUTUB FIBRE.-I find in a Dublin paper that the bristles imported for the purpose of making brooms for sweeping the streets, come from the Arenga or Gomuto palm. Is this not an error?-GOMUTO. [3951]-BAMBOO NUTS.-I wish to know what kind of nuts are the "Bamboo nuts," I find mentioned in the cir[3933.]-HYPOPHOSPHITE OF IRON AND QUININE.cular of Messrs. Mandy, Horley and Co., last number of our Will any brother reader kindly inform me of the medicinal MECHANIC, and what is the use of those nuts?-GEORGES. properties, doses, and cost of the above preparation of iron [3952.]—LOAM PANS:-Having some of these to make and quinine?-MAY. occasionally, and much annoyed with them veining inside, I shall feel obliged if any of our brother readers, having practical experience in moulding the same, will inform me the cause and remedy.-INQUIRER. [3934]-ORGAN ACCORDION STAND.-Will any fellow subscriber furnish me with a diagram for the construction of the above, so that it may be played with both hands-the feet, by means of a pedal, giving necessary action to the bellows?-SIGMATAU. [3935.] DISSOLVING SHEEP'S HORNS.-Could any of your numerous readers inform me how, or in what way, I could dissolve sheep's horns to make them into glue, size, &c., or for any manufacturing purposes ?-VERY OLD SUB SCRIBER. W. C. S. [3953.]—COIL.-As I am afraid I have annoyed Mr. A. E. Tucker more than I ought, perhaps "Sigma" would kindly answer me one or two queries. I quite forgot to state formerly that I intended making my coil in four sections. What would be the best way to connect them at the discs. I can almost fancy from "Sigma's" note in the last number of the MECHANIC that there is a possibility of doing without so much gutta [8936.]-FAST COLOUR FOR SHEEPSKINS.-Will percha paper, as I see recommended by everyone. I only hope one of your readers kindly inform me how to dye the wool of he may show me how to begin, I'll be a willing pupil. I have sheepskins (fast colour) without injury to the pelts? taken Mr. Tucker's advice, and intend putting 81b. No. 36 wire instead of 4lb; will "Sigma" also say if I should get the new double mercury break instead of Mr. Ladd's spring core inbreak. I may state here that my old coil had a stead of in., as put in my note. (This is in reference to Mr. E. Tucker's reply to my last query, which I have to thank him for.)-D. FORBES. [3954.] SCREW AND WHEEL CUTTING LATHE-Would "J. K. P." or any of your numerous correspondents kindly give me their opinion on the following:wheel-cutting lathe made expressly for me, and I want it to I am going to have a 4in. back-geared self-acting screw and be as near to perfection as possible without being too complicated. 1. Would a 3ft. 6in. bed 4in. across be the size (please give all the other dimensions)? I should like it that length. 2. What size and rate should the screw be which goes inside the bed? it must be inside. 3. What size should the mandrel be, and what length; is a thread the right size to be as strong as necessary? 4. What size and number of teeth should the back gear wheels and pinions be? 5. The slide rest must have self-acting surfacing motion, what length should the bottom slide be, what length the top one, and what is the best form of tool holder for the slide rest: 6. What is the best wheel-cutting apparatus to fit in the slide rest to cut wheels up to 34in. in diameter? The most approved plan, I believe, for dividing the head is a tangent wheel fixed to the mandrel, and the screw which turns it to have a hand and dial; or is the rows of holes the best after all.-P. N. HASLUCK. [3938.]-AMERICAN CLOTH BAG.-Having to use in [3939]-ELECTROTYPING.-Will any one please inform a a projection on that axle, d is a projection on the end of the [3941. MARKING INK.-Can any one tell me how best [3955.]-SCALE PARAFFIN.-Can any of your readers inform me how many tons of scale paraffin are produced in Scotland in one year?-S. P. [3956.]-CHEMICAL.-Will Mr. G. E. Davis be so kind as to show how I could calculate the weight in grammes of 1 litre of methyl gas at 20°C. and 760mm. pressure; and also how to prepare acetic acid from the following: Cн ̧Ï‚ н ̧Ó, CaO, H2SO, K2CгO1, Na2CO2?—R. TERSET. [3957.]-POWERS OF NUMBERS.-Will Mr. Biggs, or some other contributor to our valuable paper, be kind enough to inform me how numbers are raised to their 36th and to their 17th powers. Take No. 10 for instance, to the 36th power 3982. how is it done?-ECONOMY. [3958.]-NAMES OF PARTS OF BELLOWS.-Would any maker of Reverte's bellows and hearths, be kind enough to give me the names, separately, of all parts of bellows, such as is used in a ship building yard ?-E. FOWLER. [3959.]-THE "EDINBURGH" VELOCIPEDE.-Will any brother subscriber give the address of the maker of the "Edinburgh" velocípede ?-C. T. › [3960.]-THE BLOOD.-I beg to ask through your valuable journal, if some kind reader would give me a recipe (cheap) for purifying the blood?-J. G. JACKSON. [3961.]-BISULPHIDE OF CARBON PRISM.-Will any brother reader state what cement will resist the action of bisulphide of carbon? I have made a prism, but the bisul alters does the position of the magnet pole change with it ? filling and then re-digging? Has any condition of ground to Phide dissolves all the cements I have tried P-E. C. MURRAY. VIBRATOR. [3926.]-FORCING WATER-An engine forces water through a 9in. pipe, perpendicular, to a height of 30ft., will it require the same power to force it to the same height through a 9in. pipe, but such height being 180ft. away, with a gradual ascent of 1ft. in 6ft. ?-B. S. M. G. H. [3927.)-WINDOW PAINTING. I shall be very grateful to any of your readers who will tell me of a rich transparent permanent crimson; also a pure bright yellow ? Crimson lake is such a varnishing colour it will not bear continued exposure to daylight, the colours are to be used with oil and varnish for glass painting. Amongst all the varied and valuable information contained in your journal, I have never noticed any on the old aet of window painting, I do not rican the modern process of staining. I have been a painter of dissolving views for years, but I should be most thankful if you could assist me in the former matter.-SABLE. [3928-RE-MANUFACTURING INDIA RUBBER-Will some reader kindly tell me if india rubber of first-class quality, in sheets of in. thick and under, could be re-manufactured, and what it would be worth per pound?-J. T. [3929-EMIGRATION.-I should be pleased to get all the information I could respecting New Zealand and Tasma [3962]-WHITE LEAD.-I bought some stuff for "white lead genuine," but find it has all dried up. like old putty, [3943.]-BEES.-I have a hive of comb in which a swarm although at first it looked like ordinary white lead, and has died last winter. Can any of your readers tell me is I may been kept covered up in water; how is this?-H. safely hive a coming swarm into it this summer, I may men- [3963]-OAK, WALNUT, AND MAHOGANY STAINS. tion the hive is a common straw one with a wooden box-Would some reader supply me with recipes for making under it quite full of comb, and is 3 years old. I feel doubt- oak, walnut, and mahogany stains?-ZEMBLA. ful in consequence of the comb being apparently dirty; it appears on the outside quite black, though I see no appearance of mould. Would it do to remove any of the comb to make room for the new swarm, as it is quite full. Some hints on the general management of bees by a practical bee keeper might prove interesting to many of your readers, as they would to me.-S. W. [3914.] ARITHMETICAL QUESTION-Will Mr. J. Sharp, who answered query No. 3710, p. 213, kindly show how it can be proved that a circle is equal to a parallelogram whose length is equal to half the circumference, and breadth equal to half the diameter. If he can prove it by geometry, will he kindly do so?-T. J. O. C. [3945.-PAINT FOR BOATS.-Would any reader inform me how to mix a bronze or copper-coloured paint for the bottom of a small model boat ?-A MODEL BOAT MAKER. [3964) CAST IRON FOR TURNING.-I should be much obliged to "J. K. P." if he would give me a few hints about preparing cast iron for turning and former, I should like to know the shape of chisel, and filing, whether by chipping or pickling it. If the mode of using. If pickling be the better way, I wish to know the strength of acid, and time of duration of using it. I should also be much obliged by advice as to rebronzing a medal. It is one of a case of Napoleon medals, and the colour has been taken off by my attempting a cast in wax for electrotyping, leaving it a dull leaden colour. I should like to know how to get a cast from it for electrotyping, as wax sticks to the metal and breaks. Plaster of Paris makes a pretty good one, but I do not know how to make it conduct ing, as the plumbago will not adhere.-FADER. |